This application claims the priority of Korean Patent Application No. 2002-75395, filed on Nov. 29, 2002 in the Korean Intellectual Property Office. The disclosure herein is incorporated in the above reference entirely.
1. Field of the Invention
The present invention relates to syntheses of cathode materials for lithium batteries, particularly, a method of preparing lithium-chromium-manganese oxides having α-LiFeO2 structure.
2. Description of the Related Art
There have been reports on layered lithium-chromium-manganese oxides (LiyCrxMn2−XO4+z) as disclosed in U.S. Pat. No. 5,858,324. Conventionally, layered lithium-chromium-manganese oxides were calcined under argon (Ar) or nitrogen gas (N2) atmosphere that will raise the manufacturing cost. In addition, the material prepared by the conventional method exhibited 120 to 190 mAh/g capacity with relatively poor cycling retention. Recently, J. R. Dahn et al. reported novel lithium-chromium-manganese oxides, [Li[CrxLi(1/3−x/3)Mn(2/3−2x/3)]O2 (00.0≦X≦1.0) with α-LiFeO2 structure, give a stable capacity of about 200 mAh/g in the Journal of the Electrochemical Society, 149(11), A1454-A1459, 2002.
In order to synthesize the above-described oxide, Dahn et al. dissolved lithium salts, manganese salts, and chromium salts in distilled water and dropped ammonia solution (NH4OH) until the pH of the solution becomes 10 and the precipitation completes. After that, the precipitation was put in a muffle oven and dried in air at 130° C. overnight. The dried precipitate was heated in air at 480° C. for 12 hours. Then the resultant powder was pressed into pellets and calcined under argon (Ar) atmosphere at 900° C. for 3 hours.
According to the above method, a stabilized layered lithium-chromium-manganese oxide could be obtained. However, it requires tedious pH adjusting process, overnight oven treatment, argon (Ar) atmosphere that raises manufacturing cost.